1. Field of the Invention
The present invention relates to rubber shock absorbers for mooring guards used to protect boats and ocean or river dock structures such as quays, jetties, mooring posts, etc. These rubber shock absorbers are generally placed between the stationary part of the dock such as the vertical wall of a quay and a protective shield distributing the mooring stresses exerted by the boat or ship over a plurality of shock absorbers and distributing the reactions of the latter over a sufficiently wide surface area of the hull to avoid deformation thereof.
2. Description of the Prior Art
Rubber shock absorbers consisting of hollow elements in the form of sleeves or tubular cylindrical rolls or in the form of elongated sections having a trapezoidal transversal section have already been used for this purpose. If these shock absorbers have suitable dimensions, their curve of deformation under compression will be such that the bending which occurs is at first approximately proportional to the stress, the shock absorber accordingly having increasing stiffness to counteract elastically minor stresses. Thereafter, the bending must increase more rapidly than the stress exerted so as to resist average stresses by elastically straightening itself up without the action exerted on the boat being exaggerated and risking damage to the hull. Then, at the termination thereof, when the possibility of bending the shock absorbers is practically eliminated, the compression stiffness increases considerably once again so as to protect the mooring guard and the dock structure to the limit of admissible stress.
However, the mooring stress exerted by a boat on the guard is rarely purely perpendicular to the mooring plane. It is often oblique and it gives rise to tangential components in the absorbers, that is, parallel to the bearing faces of the absorbers. Shock absorbers in the form of tubular rolls or elongated sections having a trapezoidal section are not suitable for resisting these tangential components; their resistance or stability is insufficient when these components are transversally directed as the rolls tend to roll themselves and the trapezoidal sections tend to rest on their sides. On the other hand, their resistance is too great when these tangential components are directed longitudinally with respect to the direction of the shock absorbers.
The use of shock absorbers in the form of cylindrical hollow sleeves has also been proposed. These operate by axial compression between their bearing surfaces under the action of a mooring stress normally exerted on the shield and/or the quay. This type of absorber first counteracts any minor stresses through compression and then as the stress increases, buckling occurs towards the outside of the walls of the sleeve accompanied by stabilization or reduction of the stiffness to the point of almost total crushing, at which point the stiffness increases rapidly. Once again, these shock absorbers have a low resistance to oblique or tangential stresses which tend to lay them on their sides.
Shock absorbers have also been proposed in which a conical hollow rubber element rests at its ends on bearing surfaces which are oblique or even parallel to its axis such that the rubber element is telescopically deformed by an axial stress operating with a shearing action or with shearing and compressing combined. The load/deformation curve of this type of shock absorber under increasing axial stress is more progressive and this stiffness may be proportioned by selecting the conical shape of the element and the inclination of the bearing surfaces so as to cause the rubber to work either mainly with a shearing action (minimal stiffness) or by compression (considerable stiffness). However, with this type of conical shock absorber, it is generally necessary to laminate the rubber element with metal plates to provide it with lateral stability which produces far more costly parts than the homogeneous molded rubber parts. The rubber/metal connections thereof are also more subject to deterioration with age. In addition, the lateral deformation capacity and thus the absorption of tangential components of oblique stresses are compromised by the need to obtain satisfactory axial bending paths.